A conventional optical disk includes a plastic base upon which layers of various materials, such as metals, alloys, or dielectrics, are applied. One method of applying the layers of materials is to use a sputter deposition process.
A conventional sputter deposition process is performed using a plasma formed in a vacuum chamber of a sputter deposition system. The plasma is generated by applying electric power to a low pressure gas in the vacuum chamber. Ions originating within the plasma bombard a target formed of a material that is to be deposited on the optical disk. The bombarding ions eject material from the target. The ejected material deposits in a layer on the disk.
A conventional sputtering system known as the BALZERS.TM. BIG SPRINTER.TM. is believed to include a loadlock between a main vacuum chamber and a disk loader robot. The disk loader robot includes two opposing arms, each of which includes an identical disk holder. An external robot loads an unprocessed optical disk (or other substrate) into the disk holder, and unloads a processed disk from the disk holder. The disk loader robot rotates 180.degree., and thereby alternatively positions each disk holder at the loadlock and the external robot.
During the sputtering operation, the two masks, one known as an inner mask and one as an outer mask, prevent deposition on the central and peripheral portions of the disk, respectively. The inner mask consists of a solid cylindrical body with an annular head attached to one end of the cylindrical body. At the outside of the cylindrical body is a spring mechanism that traps the disk under the annular head. The outer mask is in shape of a flat ring. The disk holders and the carrier arm hold the masks using magnets. The annular head of the inner mask and the surface of the outer mask that faces in the same direction as the sputtered surface of the disk both get a coating of the sputtered material. Magnetized components of the disk holder and the carrier arm contact the sputtered surfaces of the inner and outer masks during loading and handling processes.
The sputter-coated inner and outer masks need to be replaced periodically. To do this, the disk loader robot is rotated 90.degree., thereby placing the disk holder with the masks that are to be replaced at a station dedicated to changing of the masks.
There are drawbacks to the above described system that heretofore have not been resolved. First, contacting the sputtered surfaces of the inner and outer masks dislodges sputtered material from the masks, causing particulate contamination on the disk and in the sputtering system. Second, the masks get hot in the vacuum chamber, and have limited opportunities to cool. The hot masks can cause heat damage to the surface of the disk. Third, the use of magnets near the substrate to hold the masks affects the plasma, thereby affecting the uniformity of the film. Fourth, the sputtering system includes a station dedicated to changing of the masks, which consumes valuable space in the machine.